In communication systems there is a never-ending search to increase the efficiency of utilization of communication system assets. A typical problem in voice-based communication systems is to increase the number of conversations that can be carried in the same bandwidth. The solution to this problem has been approached from a number of different perspectives. In one such well-known solution, information theory is used to assign short symbols to encode more frequently occurring aspects of speech and relatively longer symbols to encode less frequently occurring aspects. By efficiently coding speech, more conversations can be carried in a given bandwidth.
Similar concerns have been encountered in new voice-based communications environment—Voice over Internet Protocol (“VoIP”) service. This invention applies to the operations of VoIP on Forward Packet Data Channel (“F-PDCH”) in CDMA2000 1xEV-DV (“1x Evolution for Data and Voice”) systems. In 1xEV-DV, the F-PDCH encoder packet (EP) size can be one of the seven possible values: 216, 408, 792, 1560, 2383, 3096, or 3864 bits. The voice payload, on the other hand, is much smaller than the EP size. For example, the Enhanced Variable Rate Codec (EVRC) produces 171, 80 and 16 bits per 20 ms for rate 1, rate ½, and rate ⅛, respectively. Active speech is encoded at rate 1 or rate ½, and background noise is encoded at rate ⅛. Typically rate ⅛ is used for about 60% of the time during a conversation due to the nature of speech in which there are frequent gaps of background noise which, when taken together, comprise a relatively large part of speech. Comparing the voice payload to the EP size, it is obvious that transmission of rate ⅛ VoIP packets on the F-PDCH is extremely inefficient, wasting a large portion of the system resources while providing minor gain to the voice quality. Bundling many rate ⅛ VoIP packets into one encoder packet can improve the packing efficiency, however, doing so will increase the overall end-to-end delay of the voice communication and adversely impact the voice quality.
Thus, those skilled in the art seek improved methods and apparatus for supporting VoIP service in CDMA systems, particularly apparatus and methods that use bandwidth assets more efficiently. For example, those skilled in the art seek apparatus and methods that take into consideration the fact that a large portion of speech comprises gaps of background noise that convey little or no information, and thus which need not be reproduced with a high degree of fidelity, if at all.